Technical Field
The present invention relates to a method of preparing a metal-doped zeolite catalyst with a modified topology (e.g. a pillared zeolite or a delaminated zeolite), and a process for converting an alkyl-aromatic hydrocarbon stream to BTX (benzene/toluene/xylene) using the metal-doped zeolite catalyst.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Mandatory regulations limiting aromatic content in gasoline are the driving force to explore alternative routes for utilizing heavy aromatics produced from catalytic reforming of naphtha. One economically viable option is to convert the heavy reformate stream, which is rich in heavy aromatics (mainly C9+ aromatic compounds), to xylenes [T. C. Tsai, S. B. Liu, I. Wang, Catal. Surv. Asia 13 (2009) 94-103]. The conversion process, catalyzed by zeolites, comprises transalkylation and disproportionation reactions via a bimolecular reaction intermediate (biphenyl methane carbenium ion intermediate). Scission of ethyl and propyl side chains (dealkylation) from C9+ aromatics are important routes leading to the formation of xylenes [S. Ali, M. Ali, K. Al-Nawad, C. Ercan, Y. Wang, Appl. Catal., A. 393 (1-2) 96-108; T. C. Tsai, 1. Wang J. Catal. 133 (1992) 136-145; J. Das, Y. S. Bhat, A. B. Halgeri, Catal. Lett. 23 (1994) 161-168].
Research studies on transalkylation reactions over different zeolites with or without incorporation of metals have been reported in the literature. Use of various medium-pore zeolites such as ZSM-5 [S. A. Ali, K. Ogunronbi, S. Al-Khattaf, Chem. Engg. Res. Des., 91 (2013) 2601-2616], NU-87 [S. Park, H. Rhee, Catal. Today 63 (2000) 267-273], and MCM-22 [S. Park, H. Rhee, Catal. Today 63 (2000) 267-273], as well as large-pore zeolites such as ZSM-12 [T. C. Tsai, S. Liu, I. Wang, Appl. Catal. A: Gen. 181 (1999) 355-398; T. C. Tsai, W. H. Chen, S. B. Liu, C. H. Tsai, I. Wang, Catal. Today 73 (2002) 39-47], faujasites [I. Wang, T. C. Tsai, S. T. Huang, Ind. Eng. Chem. Res., 29 (1990) 2005-2012; J. A. Atias, G. Tonetto, H. de Lasa, Ind. Eng. Chem. Res., 42 (2003) 4162-4173; S. Al-Khattaf, N. Tukur, A. Al-Amer, Ind. Eng. Chem. Res., 46 (2007) 4459-4467; A. Krejci, S. Al-Khattaf, M. Ali, M. Bejblova, J. Cejka, Appl. Catal. 377 (2010) 99-106], zeolite β [S. Park, H. Rhee, Catal. Today 63 (2000) 267-273; J. Das, Y. Bhat, A. Halgeri, Appl. Catal., 116 (1994) 71-79; A. Halgeri, J. Das, Appl. Catal. A: Gen., 181 (1999) 347-354], mordenite [J. A. Atias, G. Tonetto, H. de Lasa, Ind. Eng. Chem. Res., 42 (2003) 4162-4173; A. Krejci, S. Al-Khattaf, M. Ali, M. Bejblova, J. Cejka, Appl. Catal. 377 (2010) 99-106; J. Cejka, J. Kotrla, A. Krejci, Appl. Catal. A: Gen., 277 (2004) 191-199], and zeolite L [J. Cejka, J. Kotrla, A. Krejci, Appl. Catal. A: Gen., 277 (2004) 191-199], have been reported. These studies show that the dealkylation and transalkylation of C9+ aromatics are significantly influenced by the topology of the pore structure as well as the type and strength of acid sites of the zeolite catalysts. [J. M. Serra, E. Guillon, A. Corma, J. Catal. 232 (2005) 342-354].
Hydrogenation functionality may also be introduced to a zeolitic catalyst by incorporating suitable metals. Such bifunctional catalysts promote desirable reactions such as hydrogenation of coke precursors, dealkylation, saturation of cracking products, and their subsequent alkylation [T. C. Tsai, P. Chao, W. Zeng, S. Tsai, Stud. Surf. Sci. Catal., 170B (2007) 1611-1616]. Incorporation of different metals over mordenite include Pd [G. Nacamuli, R. Vogel, S. Zones, U.S. Pat. No. 5,952,536 (1999), to Chevron Chem], Re [F. Alario, E. Benazzi, U.S. Pat. No. 6,037,512 (2000), to IFP; F. Raatz, P. Dufresne, C. Marcilly, U.S. Pat. No. 4,723,048 (1998), to IFP; U.S. Pat. No. 6,096,938], Ag, Bi, Cu, Pb [W. Cheng, D. Kong, D. Yang, H. Li, Z. Zhu, U.S. Pat. No. 6,500,997 (2002), to China Petro-Chemical Corporation], Cr, W, Co [U.S. Pat. No. 5,847,256]. Serra et al. [J. M. Serra, E. Guillon, A. Corma, J. Catal. 232 (2005) 342-354] studied the conversion of heavy reformate with toluene over seven zeolites and each zeolite was impregnated with one or more metals including Re, Ni, Mo, Ga, Pt, La, and Bi. The incorporation of certain metals, such as Mo and Re, was shown to increase the xylene yield.
The process of producing xylene from a C9+ aromatic feedstock through dealkylation, transalkylation, and/or disproportionation in the presence of a zeolite catalyst is widely investigated. For example, the U.S. Pat. No. 5,847,256A, the U.S. Pat. No. 8,481,443B2, and the U.S. Pat. No. 5,030,787A references disclose a process of converting a feedstock containing C9+ aromatic compounds to a product containing C6-C8 aromatic compounds by contacting the feedstock with a zeolite catalyst, wherein the zeolite catalyst is doped with a transition metal such as platinum. Additionally, the US20050143614A1 reference discloses an isomerization process for producing para-xylene from a feed mixture of xylene and ethylbenzene by contacting the feed mixture with a MTW-type zeolite catalyst. Furthermore, a catalyst system is disclosed in the U.S. Pat. No. 9,018,121B2, wherein the catalyst system involves two beds each contains a bimetallic zeolite catalyst (ZSM-5), and the metals being selected from Pt, Re, Ag, Cu, In, Sn, and Ru.
Although catalytic reactions (i.e. dealkylation, transalkylation, and disproportionation) of C9+ aromatic hydrocarbon compounds in the presence of a metal-doped zeolite catalyst are widely understood, there has been limited research on the effect of a metal-doped zeolite catalyst with a modified topology (e.g. pillared or delaminated) on dealkylation, transalkylation, and/or disproportionation of C9+ aromatic hydrocarbon compounds, and to convert the C9+ alkyl-aromatic compounds to xylene.
In view of the forgoing, one objective of the present invention is provide a method of preparing a metal-doped zeolite catalyst with a modified topology, and a process for converting an alkyl-aromatic hydrocarbon stream to BTX (benzene/toluene/xylene) using the metal-doped zeolite catalyst.